Wireless tire condition monitoring apparatuses have been proposed that permit the driver in the passenger compartment to check the conditions of the tires of the vehicle. Typically, a tire condition monitoring apparatus includes a receiver mounted in the vehicle body and transmitters attached to the respective wheel assemblies. Each transmitter detects the pressure in the tire. In addition, each transmitter wirelessly transmits a data signal including data indicating the condition of the tire from the transmission antenna.
The receiver receives signals transmitted from the transmitters. Then, the receiver displays information on the pressure of the tires on the display provided in the passenger compartment, as necessary. The tire condition monitoring apparatus preferably identifies which of the tires has the transmitter that has transmitted the received data signal. In other words, the receiver preferably identifies the position of the wheel assembly associated with the received data signal.
Patent Document 1 discloses an apparatus that identifies in which of the wheel assemblies each transmitter is provided. In this apparatus, the transmitters each send the rotation angle of the corresponding wheel assembly to the receiver by a radio signal. Each time the receiver receives a radio signal, it obtains the rotation angles of the wheel assemblies from rotational position detecting sections. The receiver monitors changes in the relative angles between the rotation angle received from each transmitter and the rotation angles obtained from the rotational position detecting sections when the rotation angle is received from each transmitter. Then, the receiver identifies the wheel assembly with the smallest change in the relative angle as the wheel assembly provided with the transmitter that has transmitted the radio signal.